This invention relates to a developing apparatus for use in an electronic photographing apparatus, such as an electronic copying apparatus, a facsimile, or a printer, and, in particular, to a developing apparatus for developing an electrostatic latent image into a visible representation by use of a one-constituent developing agent or the like.
In the conventional electronic photographing apparatus, the cascade method and the magnetic brush method, are the primary development methods employed.
In recent times, a method for effectively developing an image to be printed in a superimposed fashion, that is, for developing an electrostatic latent image on the surface of an electrostatic latent image formation area in a non-contact fashion, has extensively been studied in view of the current preference for color image recordings.
Conventionally the method of this type is generally called a non-contact developing method as achieved by a developing apparatus of FIG. 1.
In this developing apparatus, elastic blade (coating blade) 4 is pressed against development sleeve 2, to form a uniform layer of a toner T thereon. The toner layer is triboelectrically charged upon passing between development sleeve 2 and elastic blade 4.
As is shown in FIG. 2, development sleeve 2 is positioned, by a pair of gap adjusting rings 8, relative to photosensitive drum 6, which provide a small gap G therebetween, so that the layer of the toner T faces an electrostatic latent image in close proximity thereto. A bias voltage is then applied between development sleeve 2 and photosensitive drum 6, to cause to the toner T on development sleeve 2 to fly across gap 4 and attach itself to the electrostatic latent image on drum 6. Toner T attaches itself only to a high-voltage area of the electrostatic latent image, never to a low-voltage area thereof. More specifically, if the bias voltage applied across sleeve 2 and drum 6 is a D.C. bias voltage, that part of toner T which faces the low-voltage area remains on sleeve 2. On the other hand, if the vias voltage is an A.C. bias voltage, that part of toner T which faces the low-voltage area moves toward drum 6 but is immediately drawn back onto sleeve 2. In either case, that part of toner T which faces the high-voltage area moves from sleeve 2 to drum 6 and is deposited on the high-voltage area. In this way, toner T selectively attaches itself to the electrostatic latent image, to develop it into a visible image.
Conventional development sleeve 2, being of simple hollow-cylindrical type, is structually weak when a bending force is applied thereto. The development sleeve, when pressed by elastic blade 4, develops a warp S, as is shown in FIG. 2 due to pressure f exerted by elastic blade 4 thereon.
When the development position B=0.degree. as shown in FIG. 3, when elastic blade 4 is pressed from the angular position 90.degree.+.alpha..degree. to the position of development sleeve 2, then a variation in a gap G resulting from the warpage of development sleeve 2 is represented by S sin .alpha..
In this way, the gap G between photosensitive drum 6 and development sleeve 2 varies due to a warp S of development sleeve 2 by an pressure from elastic blade 4, thus causing the gap G to becomes narrower than its predetermined value. As a result, there is the problem of a poor quality image at the time of development.
Development sleeve 2, if being made "solid" as distinct from "hollow", undergoes less warpage, but the weight of the resulting structure is increased by that extent.
In the conventional developing apparatus using a magnetic two-component toner or a magnetic one-component toner, a magnet is located inside the development sleeve. It is therefore impossible to locate any reinforced member inside the development sleeve.